1. Technical Field
The present invention relates to a sensor device.
2. Related Art
There are known sensor devices which, for example, measure the state of corrosion of a reinforcing bar in concrete (e.g., see Japanese Laid-Open Patent Publication 6-222033).
Typically, the concrete in a concrete structure immediately after construction exhibits a strong alkalinity. For this reason, the reinforcing bars in a concrete structure immediately after construction have a passivation film formed on the surface thereof and are therefore safe. However, in concrete structure that is affected after construction by acid rain, exhaust gas, and the like, the concrete will be gradually acidified, and the reinforcing bars will therefore corrode.
For example, in the device recited in the above mentioned publication, a probe provided with a reference electrode and a counter electrode is embedded in concrete and measures the polarization resistance and changes in electric potential caused by the corrosion of the reinforcing bars, whereby the corrosion of the reinforcing bars is predicted.
In such a device, the reference electrode and the counter electrode embedded in the concrete are used to measure the self-potential of the reinforcing bars, which are used as a working electrode, but a corrosion response does not progress when the surfaces of the reinforcing bars do not have sufficient moisture. For this reason, in some cases, when the surfaces of the reinforcing bars do not have sufficient moisture, even though a reinforcing bar may have a corroded region, no difference (gradient) in electric potential between the corroded region and the non-corroded region occurs. In view of such a fact, in the device recited in the above mentioned publication, a fluctuation in moisture inside the concrete has a major impact and there is a variance to the self-potential (gradient) of the reinforcing bars, thus rendering it difficult to accurately predict the corrosion of the reinforcing bars.